Visual landing guidance systems for aircraft are widely used throughout the world as an aid for guiding an aircraft in descent to a runway. Such systems include the medium intensity approach lighting system with runway alignment indicator lights (MALSR), developed by the United States Federal Aviation Administration (FAA). In general, MALSR provides visual guidance to landing aircraft in an approach area of an active landing runway. More specifically, MALSR provides visual information regarding the lateral position of approaching landing aircraft relative to the location of the runway centerline and thereby enables an aircraft pilot to acquire the runway centerline well in advance of landing the aircraft, especially in low visibility conditions.
A typical MALSR includes a combination of three independent guidance lighting arrays that are laid out on a runway approach and that include a threshold array, a steady-burning array, and a sequenced flasher array. FIG. 5 depicts a typical MALSR lighting arrangement. The threshold array includes 18 to 32 steady-burning light sources that are arranged in a line perpendicular to the centerline of the runway, at the threshold of the runway. The steady-burning array includes nine light bars, each having five steady-burning light sources mounted thereto. Seven of the lightbars are evenly spaced at intervals of 200 feet, beginning 200 feet from the runway threshold. The other two lightbars, or wing lights, are disposed on either side of the lightbar at the 1,000 foot mark. The sequenced flasher array includes 5 to 8 flasher light sources that are evenly spaced at intervals of 200 feet, beginning 1,600 feet from the runway threshold. In operation, the sequenced flasher array gives the appearance of a rolling ball of light headed toward the runway down the centerline thereof. The lighting arrays operate in accordance with an off mode and an on mode having three different levels of lighting intensity—low, medium, and high.
Unfortunately, however, current MALSR's are susceptible to relatively frequent electrical failure. For example, the circuitry and components of MALSR's are susceptible to severe direction swings and magnitude surges in transformer excitation currents, typically caused by unintentional simultaneous operation of two of the three lighting intensity levels when switching between the different levels. These swings and surges yield damaging electrical transients that lead to overstressing and premature failure of transformers, switch contactors, control circuit boards, the lamps and the like. Moreover, the lightbars are particularly vulnerable to lightning strikes, which fault out the MALSR. As a result of the above types of electrical failures, the MALSR must be diagnosed and repaired to return the MALSR to normal operation, which can take hours or days. Diagnosis, repair, replacement of prematurely failed components, or simple reset of the MALSR creates guidance system down-time that, at best, is time consuming and expensive, and, at worst, increases the risk of landing an aircraft.